We wish to determine whether there are unique antigens in the circulation of patients with systemic lupus erythematosus derived from surface membranes of lymphocytes and other more primitive hematopoetic cells. Since the cryoglobulins obtained from systemic lupus erythematosus serum contain antilymphocyte antibodies, it is not unreasonable to expect that such antigens would be present also. In preliminary experiments, immunization of rabbits with SLE cryoglobulins has demonstrated that the antisera will react with both normal and SLE lymphocytes. Some antisera are exclusively reactive with SLE lymphocytes. Studies in progress are attempting to define the lymphocyte determinants with which these antisera react in an attempt to demonstrate the cells of origin and their relationship to any pathogen responsible for the initiation or perpetuation of SLE.